Wire electrode for electric discharge lamps



Feb. 17, 1959 w. SCHILLING' ETAL' 2,

WIRE ELECTRODE FOR ELECTRIC DISCHARGE LAMPS Filed Feb. 14, 1955 FIG. 2

FIG.3

INVEN R S:

' a Mm United States Patent (iermany, assignors to Patent-Treuhand-Gesellschaft fur Elektrische Gliihlampen m. b. H., Munich, Germany Application February 14, 1955, Serial No. 487,926 Claims priority, application Germany February 26, 1954 2 Claims. (Cl. 29-420.5)

Our invention relates to a wire electrode for electric vapor or gaseous discharge lamps which electrode is provided with emission material. In case of such electrodes it is important to increase the receiving capacity for emission materials of the electrode wires consisting generally of tungsten or molybdenum. Usually, such electronemitting material consists of alkaline earth metallic oxides to which are added, for instance, compounds of elements of the 4th and th group of the periodic table. Such an electrode can be a straight wire or it can consist of a wire which is coiled to a single coil or, if desired, to a multiple coil. In such a case the emission material sits predominantly between the windings of the inner coil which is wound with interspaces.

An object of our invention is to provide the Wire with such a surface that a greater quantity of emission material adheres safely to it. For this purpose the wire should be provided with a very rough surface which has cracks 3:151 spaces serving for holding fast the emission matell According to the present invention this latter purpose is obtained in such a manner that a wire produced of sintered metallic powders, preferably of tungsten or molybdenum, and having a fiber structure is distorted over its whole length, i. e. to such a degree that there are formed cracks and spaces on the wire surface in consequence of a separation of the crystal fibers.

For a better understanding of the present invention reference should be made to the accompanying drawing which shows by way of an example Wire electrodes in a part view and in a very enlarged scale. Fig. 1 shows a wire electrode of well-known art consisting of straight wire. Fig. 2 shows a corresponding wire electrode according to the present invention. Fig. 3 shows an electrode of coiled wire of well-known art, and Fig. 4 shows a corresponding coiled electrode made of a wire which is treated according to the present invention.

In case of tungsten or molybdenum wires manufactured as usually by sintering metallic powders with sub sequent hammering, rolling or drawing a fiber structure is obtained. Thereby the crystal fibers 6 being brought into a straight form are running parallel to the longitudinal axis 5 of the wire as shown in Fig. I. In Fig. 2 there is shown a part of a wire electrode as described in the present invention. After distorting the whole Wire around its axis 5 the crystal fibers 7 are now running in a helical form. If such a distortion is made strong enough, i. e. so that the outer fibers 7 of the wire are running against its axis 5 Within an angle or of to 70, suitably of 30 to 50', then a rough surface will be obtained. Obviously, such a rough surface is brought about because the outer fibers separate from one another whereby cracks and spaces are formed.

It is well known that a very little torsion is caused by coiling the Wires. But the angles of such a torsion amount to 2 to 3 only, in exceptional cases to 7 at the most. But such a little torsion does not sufiice to separate the outer fibers of the wire in the desired manner and to terialcan well adhere.

scribed in the present invention is distorted so much' 2,873,518 Patented Feb. 17, 1 959 bring about a rough surface to which the emission met- In contrast thereto the wire dethat the aforesaid angle amounts to at least 15 i For the manufacture of wires 'to be distorted as described in the present invention such a material has to be chosen which has a fiber structure. Thats the case ifthe manufacture is made in the usualway by sintering metallic powder which is thereupon hammered, rolled and drawn. Such a distorting of the straight wire is suitably made at a simultaneous heating up to 200 to 250 C. Thereby the outer fibers of the wire are wound like ropes upon the intact wire core and separates slightly from one another so that the desired cracks and spaces are formed.

Preferably, the distorted Wire is coiled to a single or to a multiple coil but attention should be paid to the necessity that the little orsion caused by the coiling itself be not directed against the original strong torsion because the proportionately fragile wire could then break.

Fig. 4 shows an electrode the wire of Which distorted as described in the present invention has been coiled after distortion. It is clearly to be seen that the outer fibers 7 are running in a helical form around the wire. In contrast thereto Fig. 3 shows a coiled electrode consisting of a well-known non-distorted wire. There the outer fibers 6 are running nearly in the direction of the wire axis.

The emission material is applied to the wire electrode in such a manner that it is contained principally on the wire surface and in the gaps between the outer fibers of the wire which gaps are caused by the distortion, and perhaps in the spaces within the coil Wound at first which has a small coiling diameter, i. e. within the primary coil. It has been found that the emission material applied in the above mentioned manner is held fast in a sufficient quantity to supply electrons during 10,000 and more operating hours and to increase the life of those lamps provided with these electrodes by 50 and more percent. It is obvious that thicker layers of emission material filling perhaps also the second coil, the so-called secondary coil, would be held not so fast by means of adhesion by the emission material in the wire gaps and in the primary coil and, therefore, such layers would incline to sputter under the influence of the discharge.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A method of manufacturing a wire electrode which method consists in sintering metallic powders selected from the group consisting of tungsten and molybdenum to produce a rod or wire, reducing and elongating said wire to produce a fiber structure of the wire crystals parallel to the longitudinal axis of the wire, distorting the wire along its longitudinal axis at a simultaneous heating up to 250 C. so that the outer fibers of the Wire are running against its axis within an angle of 15 to 70 whereby cracks and spaces are formed by separation of the crystal fibers on 'the wire surface over its whole length, thereby forming a rough surface to which the emission material can well adhere.

2. A method of manufacturing a wire electrode which method consists in sintering metallic powders selected from the group consisting of tungsten and molybdenum to produce a rod or Wire, reducing and elongating said wire to produce a fiber structure of the Wire crystals parallel to the longitudinal axis of the wire, distorting the wire along its longitudinal axis at a simultaneous heating up to 250 C. so that the outer fibers of the wire are running against its axis within an angle of 15 to 70 whereby cracks and spaces are formed by separation of the czystalfibers on the, wire surface. over its whole, length, thereby forming a rough surface to which the emission material can well adhere, and in coiling the wire to a single; or multiple coil whereby the ceiling is: made in; such amanner that the little torsion caused by the coil.- ing itselfis not directed against the-course of theoriginal strong torsion.

References Cited in thefile of this patent;

4 Hunter -July 30,v Ross Nov. 10, Francis Oct. 31, Spanner July 15, Aicher July 18, Warnke Nov. 21, Litton Sept. 28, Williams -Jan. 13, Rigden June 5, 

